Cosmic cartographers find 'great wall.'Cosmic Cartographers Cartography is the study of map making and cartographers are map makers. Before 1400
Two astrophysicists An astrophysicist is a person who professionally studies and conducts research in astrophysics. Famous astrophysicists
Astronomers Famous astronomers and astrophysicists include:
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adj. chop·pi·er, chop·pi·est
Having many small waves; rough: choppy seas.
[From chop1. ocean looks smooth from a space shuttle space shuttle, reusable U.S. space vehicle. Developed by the National Aeronautics and Space Administration (NASA), it consists of a winged orbiter, two solid-rocket boosters, and an external tank. , the universe as a whole should appear uniform, despite occasional small structures like galaxies.
The astronomical survey Astronomical surveys generally involving imaging or mapping of regions of the sky using Telescopes. The surveys are usually restricted to one band of wavelengths of electromagnetic radiation (e.g. light or radio) or to measurements of the flux of one type of particle (e.g. , conducted by Margaret J. Geller and John P. Huchra of the Harvard-Smithsonian Center for Astrophysics The Harvard-Smithsonian Center for Astrophysics (CfA) is located in Cambridge, Massachusetts. It consists of the Harvard College Observatory and the Smithsonian Astrophysical Observatory. The Center is located at 60 Garden Street. in Cambridge, Mass., looks at larger slices of the universe than any previous survey. Even at this scale, galaxies group together in surprisingly coherent arrangements, they report in the Nov. 17 SCIENCE.
Guided by a two-dimensional map made in the 1960s, Geller and Huchra have mapped more than 11,000 galaxies in a wedge of the northern celestial hemisphere, measuring the redshift redshift
Displacement of the spectrum of an astronomical object toward longer wavelengths (visible light shifts toward the red end of the spectrum). In 1929 Edwin Hubble reported that distant galaxies had redshifts proportionate to their distances (see of each galaxy brighter than magnitude 20.5 to pinpoint its location in three dimensions. The redshift indirectly indicates an object's distance from Earth. Their ongoing survey now covers 1/100,000 of the volume of the visible universe -- comparable to a world atlas describing only Rhode Island Rhode Island, island, United States
Rhode Island, island, 15 mi (24 km) long and 5 mi (8 km) wide, S R.I., at the entrance to Narragansett Bay. It is the largest island in the state, with steep cliffs and excellent beaches. .
Stretching dramatically across the map is the Great Wall, a galaxy cluster 500 million light-years long, 200 million light-years wide and 15 million light-years thick. The vast bubbles it outlines -- nearly empty stretches of space 150 million light-years in diameter -- are equally important. "It may make more physical sense to regard the individual voids as the fundamental structures" of the universe, Geller and Huchra write. These voids threaten one theory describing the nature of dark matter -- the hypothetical material that caulks the gap between the amount of material astrophysicists detect in the universe and the much greater quantity they know must exist. Without dark matter to make up the difference, gravity couldn't hold stars and galaxies together.
Most astrophysicists believe dark matter is slow-moving, or "cold." In this standard model, galaxies form at denser regions of dark matter, as foam gathers at the tip of a wave, Geller and Huchra say. But the vast size of the newly mapped voids doesn't match the calculated distribution of cold dark matter, they report. Thus, the theory is missing "something profound," Geller says.
Not so, responds theoretical astrophysicist James E. Gunn
Since Geller and Huchra reported their first results nearly four years ago (SN: 1/18/86, p. 38), many other astrophysicists have started their own mapping projects, some scrutinizing different regions of space and others looking at already-mapped regions in more detail, Geller says. But until surveyors map a region vast enough to show conclusively whether matter is evenly distributed, she says, they cannot accurately describe the structure of the universe.